The present invention relates to a connection control method for use in a personal communication system for allowing each subscriber thereof to make a call at any terminal to any designated terminal so as to provide advanced services.
FIG. 1 is a block diagram showing the construction of a conventional communication system. In a personal communication system, subscribers 11.sub.1, 11.sub.2, 11.sub.3, and so forth are designated by unique personal numbers (which are also denoted by 11.sub.1, 11.sub.2, 11.sub.3, and so forth). Each subscriber can make a call using any terminal 12.sub.1, 12.sub.2, 12.sub.3, and so forth (the terminal numbers thereof are also denoted by 12.sub.1, 12.sub.2, 12.sub.3, and so forth). When a subscriber registers a desired terminal as a terminating terminal to a switching center, he can receive incoming calls at the registered terminal. In an example shown in FIG. 1, the terminals 12.sub.1 to 12.sub.4 are accommodated in a switching center 30.sub.1. In the figure, a terminal 12.sub.5 is accommodated in a switching center 30.sub.2 which is connected to the switching center 30.sub.1. The switching center 30.sub.1 comprises a terminating terminal memory part M2 and a terminal idle/busy memory part M3. The terminating terminal memory part M2 stores terminating terminal numbers corresponding to personal numbers of the subscribers. The terminating terminal numbers are designated as terminating addresses by the subscribers. The terminal idle/busy memory part M3 stores idle/busy information which represents the idle state or busy state of each terminal depending on whether or not it is communicating (namely, performing an incoming/outgoing call connection process). When the connection process is started, the busy state is registered. On the other hand, when the communication session is completed, the idle state is registered.
Each subscriber can receive an incoming call at his registered terminal. On the other hand, each subscriber can make a call at any terminal regardless of whether it is his registered terminal. Unless otherwise specified, each subscriber does not have a so-called call waiting service where he can make a call at a terminal which is busy. In this example, terminating terminals of the subscribers 11.sub.1, 11.sub.2, 11.sub.3, and so forth are denoted by 12.sub.1, 12.sub.2, 12.sub.3, and so forth, respectively.
In a personal communication, when a subscriber makes a call, he inputs into a terminal both his personal number and a terminating personal number or a terminating terminal number. Thus, an outgoing call connection request takes place. The terminal sends this request to the switching center connected thereto. The switching center interrogates a service class of the subscriber corresponding to the received originating personal number from a subscriber service memory part M1. (The term "interrogate" means, throughout this specification, "retrieve and read out".) Thereafter, the switching center starts an outgoing call connection process corresponding to the service class. For example, when the subscriber 11.sub.1 makes a call at the terminal 12.sub.2, the switching center 30.sub.1 refers to the idle/busy information for the terminal 12.sub.2 stored in the terminal idle/busy memory part M3. When the idle/busy information represents an idle state, the switching center 30.sub.1 performs the outgoing call connection process. Since the terminal 12.sub.2 is a terminating terminal of the subscriber 11.sub.2, if the switching center 30.sub.1 is performing a terminating call process to the subscriber 11.sub.2 and therefore his idle/busy state is busy when the subscriber 11.sub.1 makes a call at the terminal 12.sub.2, the switching center 30.sub.1 does not perform the originating process for the subscriber 11.sub.1.
When a call is terminated to the subscriber 11.sub.1, the switching center 30.sub.1 refers to the idle/busy information for the terminal 12.sub.1 stored in the terminal idle/busy memory part M3 corresponding to the terminal number of the terminating terminal 12.sub.1 of the subscriber 11.sub.1 stored in the terminating terminal memory part M2. When the idle/busy information represents an idle state, the switching center 30.sub.1 causes the call connection control part 31 to connect the call to the terminal 12.sub.1. At this point, if the subscriber 11.sub.2 is communicating at the terminal 12.sub.1, since the idle/busy information for the terminating terminal 12.sub.1 of the subscriber 11.sub.1 represents a busy state, the switching center 30.sub.1 does not perform the outgoing call connection process.
Since each subscriber cannot make calls, simultaneously, at a plurality of terminals disposed at different locations, a service which simultaneously processes a plurality of communication requests for one subscriber should be normally restricted. In the prior art, the switching center only stores the idle/busy information for terminals. Thus, while the subscriber 11.sub.1 is communicating at the terminal 12.sub.2, if there is an incoming call to the subscriber 11.sub.1, the switching center 30.sub.1 connects the incoming call to the registered terminal 12.sub.1 of the subscriber 11.sub.1 when the terminal 12.sub.1 is idle. Thus, the condition that the same subscriber is communicating at a plurality of terminals, simultaneously, is caused, which gives rise to a problem of providing double calls to the same contracted personal number.
Now assume that the subscribers 11.sub.1, 11.sub.2, etc. have a call waiting service. In this condition, if there is a new incoming call to a subscriber who is already communicating (as a first communication), the subscriber can receive the second communication while suspending the first communication. For example, when the subscriber 11.sub.3 inputs the personal number of the subscriber 11.sub.1 at the terminal 12.sub.3, an outgoing call connection request takes place. At this point, the switching center 30.sub.1 refers to the terminal idle/busy memory part M3 corresponding to the terminal number 12.sub.1 of the terminating terminal 12.sub.1 registered by the subscriber 11.sub.1 and stored in the terminating terminal memory part M2. If the terminal 12.sub.1 is idle, the switching center 30.sub.1 causes the call connection control part 31 to connect the incoming call to the terminal 12.sub.1. When the subscriber 11.sub.1 replies to the incoming call at the terminal 12.sub.1, the first communication is established.
Next, during the first communication, when a subscriber 11.sub.4 inputs the personal number of the subscriber 11.sub.1 at a terminal 12.sub.4, a connection request takes place. At this point, the switching center 30.sub.1 interrogates the terminal number 12.sub.1 of the terminating terminal 12.sub.1 registered by the subscriber 11.sub.1 and stored in the terminating terminal memory part M2 and causes the call connection control part 31 to connect the incoming call to the terminal 12.sub.1. By suspending the first communication at the terminal 12.sub.1, the subscriber 11.sub.1 can receive the second communication which is the incoming call from the subscriber 11.sub.4. In addition, the subscriber 11.sub.1 can suspend the second communication so as to restore the first communication.
In the above-described prior art, let it be supposed that the subscriber 11.sub.1 dialed the personal number of a subscriber 11.sub.3 at a terminal 12.sub.2 other than his terminating terminal 12.sub.1 which has been in a first communication with the subscriber 11.sub.3. At this point, if the subscriber 11.sub.4 originates a call for communication with the subscriber 11.sub.1 at the terminal 12.sub.4, the call to the subscriber 11.sub.3 would be connected to the terminating terminal 12.sub.1 as explained previously. Thus, the call is not received by the subscriber 11.sub.1 who is communicating at the terminal 12.sub.2. In other words, while a subscriber is communicating at a terminal other than his terminating terminal, he cannot have call waiting service. In addition, since the subscriber is communicating at a terminal other than his terminating terminal, the switching center eventually connects an incoming call to his registered terminal where he is absent.
In an integrated services digital network (ISDN) system, which is not necessarily a personal communication system, each terminating terminal has a display 12D as shown in FIG. 1. With the display 12D, a calling line identification service which displays the terminal number of an originating terminal is performed. In this system, each switching center 30 shown in FIG. 1 comprises, as shown in FIG. 2, a call connection control part 31, a terminal number sending/receiving part 34, a terminal number transmitting part 35, and a personal number receiving part 36. The call connection control part 31 controls line connections between the switching center and terminals or line connection with another switching center. The terminal number sending/receiving part 34 sends and receives terminal numbers to and from terminal 12.sub.1. The terminal number transmitting part 35 sends and receives a terminal number to and from another switching center. The personal number receiving part 36 receives personal numbers from terminals 12.sub.j.
When an originating subscriber 11.sub.1 makes a call at a terminal 12.sub.1, he inputs both his personal number and the terminal number of a terminating terminal (for example, the terminal number of a terminal 12.sub.5 as in FIG. 1). At this point, the originating terminal 12.sub.1 sends a SETUP message to the switching center 30.sub.1. The SETUP message serves to initiate the call and contains the terminal number of the terminating terminal, the personal number of the originating subscriber 11.sub.1, and the terminal number of the originating terminal 12.sub.1. Thus, the personal number receiving part 36 and the terminal number sending/receiving part 34 of the switching center 30.sub.1 receive the terminal number of the terminating terminal, the personal number of the originating subscriber 11.sub.1, and the terminal number of the originating terminal 12.sub.1. Thereafter, the switching center 30.sub.1 analyzes the terminal number of the terminating terminal. If the terminal number of the terminating terminal is not accommodated in the switching center 30.sub.1, the terminal number transmitting part 35 of the switching center 30.sub.1 transmits an IAM message to a switching center 30.sub.2 which accommodates the terminating terminal. The IAM message contains the terminal number of the originating terminal 12.sub.1, and the terminal number of the terminating terminal.
The switching center 30.sub.2 sends a SETUP message to the terminating terminal 12.sub.5. The SETUP message serves to call the terminating subscriber 11.sub.5 and contains the terminal number of the originating terminal 12.sub.1, and the terminal number of the terminating terminal. The terminating terminal 12.sub.5 displays the terminal number 12.sub.1 of the originating terminal 12.sub.1 on the display 12D. Thus, the terminating subscriber 11.sub.5 can guess from the originating terminal number 12.sub.1 on the display 12D who the originating subscriber 11.sub.1 could be and which company or location the terminated call could be originated from.
When a call is sent from a telephone with a representative telephone number of a company or the like, it is impossible for a terminating subscriber to know by whom of the company the call is sent. When a call is sent from a mobile telephone (such as a car telephone or a portable cellular phone), if the mobile telephone is shared by several people, it is impossible for a terminating subscriber to know by whom the call is sent. In the personal communication (personal number communication) system, each subscriber is given a unique personal number and any terminal can be registered as his terminating terminal. Even if the calling line identification service of the ISDN system is introduced to the personal communication system, the terminating subscriber cannot know the originating subscriber from the originating terminal number since each terminal can be used by any subscriber. Thus, even with the terminal number of an originating terminal displayed on the terminating terminal, the terminating subscriber cannot estimate the identify of the originating subscriber. In other words, although each subscriber is given a unique personal number, it cannot be effectively used.